Disk drives are well known in the computer art for providing secondary mass storage with random access. A disk drive includes one or more magnetic data storage disks rotated on a spindle by a spindle motor within an enclosed housing. A magnetic read/write head (transducer or slider) with an air bearing surface is placed on an actuator arm and positioned close to a corresponding disk.
The close proximity of the head to the disk enables high-resolution servo patterns and user data to be recorded on the disk. The servo patterns are written in servo sectors which are interleaved between data sectors. The servo patterns provide a servo controller with head position information to enable a head positioner, such as a rotary voice coil motor, to move the head from track-to-track during random access seek operations, and to maintain the head in proper alignment with a track during track following operations when user data is written to or read from the available data sectors on the track. The servo patterns include short servo bursts of constant frequency, precisely located relative to a track centerline. The servo patterns allow the head to follow the track centerline even when the track is non-circular, as can occur with spindle wobble, disk slip and thermal expansion.
The servo patterns have been written by an external servo track writer that supports the disk drive on a large granite block to reduce vibration. However, servo track writers are expensive, require a clean room environment and expose the head and the disk to the environment. The servo patterns have also been written by the disk drive during self-servo writing without a servo track writer. Self-servo writing involves the head reading position and timing information from the disk, the head being positioned using the position information and the head writing the servo patterns to the disk using the timing information.
Self-servo writing suffers from self-propagation, as described in U.S. Pat. No. 5,907,447 to Yarmchuk et al. During self-propagation, servo bursts in a previous track are used to position the head as the head writes servo bursts to the next track. However, perturbations in the servo bursts in the previous track propagate to the servo bursts in the next track. Compound errors that propagate across the tracks can lead to excessive track non-circularity.
There is, therefore, a need to reduce compound errors due to self-propagation during self-servo writing in a disk drive.